Remote plasma radical treatment of silicon oxide

ABSTRACT

Embodiments described herein generally relate to methods for manufacturing flash memory devices. In one embodiment, the method includes generating a plasma comprising nitrogen-containing radicals in a remote plasma applicator, flowing the plasma comprising nitrogen-containing radicals into a processing region of the processing chamber where a semiconductor device is disposed, wherein the semiconductor device has a substrate comprising an oxide layer formed thereon, exposing an exposed surface of the oxide layer to the nitrogen-containing radicals, and incorporating nitrogen in the exposed surface of the oxide layer of the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 61/552,370, filed Oct. 27, 2011, which is herein incorporatedby reference.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention generally relate to manufacturingsemiconductor devices. More specifically, embodiments described hereinrelate to manufacture of floating gate NAND memory devices and othertransistor gate dielectrics using an improved plasma applicator andprocess.

2. Description of the Related Art

Flash memory, such as NAND flash memory devices, is a commonly used typeof non-volatile memory in widespread use for mass storage applications.The NAND flash memory devices typically have a stacked type gatestructure in which a tunnel oxide (TO), a floating gate (FG), aninter-poly dielectric (IPD), and a control gate (CG) are sequentiallystacked on a semiconductor substrate. The floating gate, the tunneloxide, and the underlying portion of the substrate generally form a cell(or memory unit) of the NAND flash memory device. A shallow trenchisolation (STI) region is disposed in the substrate between each celladjacent to the tunnel oxide and the floating gate to separate the cellfrom adjacent cells. During writing of the NAND flash memory devices, apositive voltage is applied to the control gate which draws electronsfrom the substrate into the floating gate. For erasing data of the NANDflash memory devices, a positive voltage is applied to the substrate todischarge electrons from the floating gate and through the tunnel oxide.The flow of electrons is sensed by a sensing circuitry and results inthe returns of “0” or “1” as current indicators. The amount of electronsin the floating gate and “0” or “1” characteristics form the basis forstoring data in the NAND flash memory devices.

The floating gate is typically isolated from the semiconductor substrateby the tunnel oxide and from the control gate by the inter-polydielectric, which prevents the leakage of electrons between, forexample, the substrate and the floating gate or the floating gate andthe control gate. To enable continued physical scaling of the NAND flashmemory device, a nitridation process has been used by the industry toincorporate nitrogen into the surface of the floating gate to improvethe reliability of the tunnel oxide or to suppress dopant diffusion outof the floating gate. The surface nitridation of the tunnel oxide isalso desirable for minimizing the flat-band voltage (Vfb) shift andmobility degradation. Therefore, the percentage of the nitrogen at thefloating gate and the tunnel oxide interface is critical to improve theNAND flash program window. For NAND Flash applications, it has beendesirable to increase the interface N % concentration from nominally 3%to much higher levels of 6%-12%, which, however, requires high thermalbudgets in excess of 1100° C. and 60 seconds. However, the manufacturersof NAND Flash memories typically prefer thermal budgets less than 1000°C. and 30 seconds to prevent the dopant in the floating gate fromdiffusing out. In addition, it has been observed that the nitridationprocess also undesirably incorporates nitrogen into shallow trenchisolation regions. Nitrogen incorporated in the shallow trench isolationregion between neighboring floating gate structures forms a chargeleakage path which can negatively impact final device performance.

Therefore, there is a need for improved methods and an apparatus withouthaving the above-mentioned issues.

SUMMARY OF THE INVENTION

Embodiments described herein generally relate to methods formanufacturing flash or DRAM memory devices. In various embodiments, themethod generally includes a radical nitridation process to incorporatenitrogen into exposed surfaces of a tunnel oxide or SiO₂ gate dielectricformed on a substrate. In one embodiment, a method for processing asemiconductor device in a processing chamber is provided. The methodgenerally includes generating a plasma comprising nitrogen-containingradicals in a remote plasma applicator, flowing the plasma comprisingnitrogen-containing radicals into a processing region of the processingchamber where the semiconductor device is disposed, wherein thesemiconductor device has a substrate having an oxide layer formedthereon, exposing an exposed surface of the oxide layer to thenitrogen-containing radicals, and incorporating nitrogen in the exposedsurface of the oxide layer of the substrate.

In another embodiment, a method for processing a semiconductor device ina processing chamber is provided. The method generally includes exposingthe semiconductor device to a nitrogen-containing gas, the semiconductordevice having a substrate having an oxide layer formed thereon and ashallow trench isolation disposed adjacent to the oxide layer, flowing agas mixture comprising nitrogen-containing gas and/or a non-reactive gasinto a remote plasma applicator, exciting the gas mixture to produce aplasma comprising nitrogen-containing radicals and/or radicals from thenon-reactive gas, flowing the plasma comprising substantially ofnitrogen-containing radicals and/or radicals from the non-reactive gasinto the processing region of the processing chamber where thesemiconductor device is disposed in the presence of thenitrogen-containing gas to activate the nitrogen-containing gas,exposing an exposed surface of the oxide layer to thenitrogen-containing radicals from the activated nitrogen-containing gas,and incorporating nitrogen in the exposed surface of the oxide layer ofthe substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 illustrates a schematic cross-sectional view of an exemplarysemiconductor device that can be made with a method and an apparatusaccording to one embodiment of the invention.

FIG. 2 illustrates a schematic view of a remote plasma system inaccordance with one embodiment of the invention.

FIG. 3 illustrates a schematic and fragmentary cross-sectional side viewof an exemplary delivery pipe for use in supplying radicals of a plasmato an RTP apparatus according to one embodiment of the invention.

FIG. 4 illustrates a schematic and fragmentary top view of a deliverypipe of FIG. 3 and an RTP apparatus in accordance with an embodiment ofthe invention.

FIG. 5 illustrates a method of fabricating a NAND flash memory deviceaccording to one embodiment of the present invention.

FIG. 6A-6D illustrate stages of fabrication of a NAND flash memorydevice in accordance with the embodiments of the present invention.

FIG. 7 illustrates a method of fabricating a NAND flash memory deviceaccording to another embodiment of the present invention.

DETAILED DESCRIPTION

The invention describes an apparatus and method for incorporatingradicals of a plasma into a substrate or a material on a semiconductorsubstrate using a remote plasma source. In general, plasma sourcesgenerated by, for example, an energetic excitation of gaseous moleculesconsisting of a plasma of charged ions, radicals, and electrons. Theinventors of the present invention recognize that radicals of a plasmareact in a much more desirable manner with silicon or polysiliconmaterial on a substrate, than ions or a mixture of radicals and ions. Inthat regard, the invention provides an apparatus and a method ofeliminating the majority of the ions of the plasma such that onlyradicals of the plasma react with silicon or polysilicon material on asubstrate, thereby obtaining a greater selectivity of processing ofsilicon or polysilicon material on the substrate.

The present invention is not intended to be limited to a particulardevice since the apparatus and methods described herein can be used forthe manufacture of semiconductor devices and structures suitable fornarrow pitch applications. As used herein, narrow pitch applicationsinclude half-pitches of 32 nm or less (e.g., device nodes of 32 nm orless). The term “pitch” as used herein refers to a measure between theparallel structures or the adjacent structures of the semiconductordevice. The pitch may be measured from side to side of the same side ofthe adjacent or substantially parallel structures. The semiconductordevices and structures may be utilized in applications having greaterpitches as well. The semiconductor devices may be, for example, NAND orNOR flash memory, or other suitable devices.

Exemplary NAND Flash Memory Device

FIG. 1 illustrates a schematic cross-sectional view of an exemplarysemiconductor device, such as a NAND flash memory device 100, that canbe made with the apparatus of the present invention. The memory device100 generally includes a substrate 102 having a tunnel oxide layer 104disposed thereon. A floating gate 106 is disposed on the tunnel oxidelayer 104. The floating gate 106, the tunnel oxide layer 104, and theunderlying portion of the substrate 102 form a cell 103 (or memory unit)of the memory device 100. Each cell 103 of the memory device 100 may beseparated, for example, by a shallow trench isolation (STI) region 108which is disposed in the substrate 102 between each cell 103 (e.g.,adjacent to the tunnel oxide layer 104 and floating gate 106, where theSTI region 108 separates the cell 103 from adjacent cells 105 and 107).The memory device 100 further includes a control gate layer 112 and aninter-poly dielectric (IPD) layer 110 disposed between the floating gate106 and the control gate layer 112. The IPD layer 110 separates thefloating gate 106 from the control gate layer 112.

The substrate 102 may include a suitable material such as crystallinesilicon (e.g., Si<100> or Si<111>), silicon oxide, strained silicon,silicon germanium, doped or undoped polysilicon, doped or undopedsilicon wafers, patterned or non-patterned wafers, silicon on insulator(SOI), carbon doped silicon oxides, silicon nitride, doped silicon,germanium, gallium arsenide, glass, sapphire, or the like. In someembodiments, the substrate 102 comprises silicon.

The tunnel oxide layer 104 may include silicon and oxygen, such assilicon oxide (SiO₂), silicon oxynitride (SiON), or high-k dielectricmaterials, such as aluminum-(Al), hafnium-(Hf), or lanthanum-(La),zirconium-(Zr) based oxides or oxynitrides, or silicon nitrides(Si_(x)N_(y)), in single or layered structures (e.g., SiO₂/high-k/SiO₂),or the like. The tunnel oxide layer 104 may have any suitable thickness,for example, between about 5 nm to about 12 nm. The tunnel oxide layer104 may have a width, within each cell, substantially equivalent to thewidth of a base of the floating gate 106. The STI region 108 may includesilicon and oxygen, such as silicon oxide (SiO₂), silicon oxynitride(SiON), or the like.

The floating gate 106 typically includes a conductive material, such assilicon, polysilicon, metals, or the like. The floating gate 106 has aconfiguration suitable to facilitate disposing portions of the controlgate layer 112 between adjacent cells (e.g., between cells 103, 105, and107). As such, the floating gate may be formed in an inverted “T” shape.As used herein, the term inverted “T” refers generally to the geometryof the structure wherein an upper portion of the floating gate 106 isrelieved with respect to a base of the floating gate 106. Such reliefprovides room for the IPD layer 110 to be formed over the floating gate106 without completely filling the gap between adjacent floating gates106, thereby allowing a portion of the control gate layer 112 to bedisposed between adjacent floating gates 106.

The IPD layer 110 may include any suitable single or multi-layerdielectric materials. An exemplary single layer IPD may include SiO₂,SiON, or a high-k dielectric material as discussed above with respect totunnel oxide layer 104, or the like. An exemplary multi-layer IPD may bea multi-layer “ONO” structure (not shown) including a first oxide layer,a nitride layer, and a second oxide layer. The first and second oxidelayers typically include silicon and oxygen, such as silicon oxide(SiO₂), silicon oxynitride (SiON), or the like. The nitride layertypically comprises silicon and nitrogen, such as silicon nitride (SiN),or the like. In some embodiments, a multi-layer IPD layer comprisingSiO₂/high-k/SiO₂ (such as, SiO₂/Al₂O₃/SiO₂) can also be used as the IPDlayer 110. The IPD layer 110 may be deposited to a thickness of betweenabout 10 nm to about 15 nm.

The control gate layer 112 may be deposited atop the IPD layer 110 toform a control gate. The control gate layer 112 typically comprises aconductive material, such as polysilicon, metal, or the like. Theinverted T shape of the floating gate 106 enables a larger surface area,located between adjacent floating gates (for example, those of cells 103and 105), for the control gate late 112. The increased surface area ofthe control gate layer 112 may advantageously improve capacitivecoupling between a sidewall of the floating gate 106 and the controlgate, and may reduce parasitic capacitance between adjacent floatinggates, floating gate interference, noise, or the like.

Optionally, prior to IPD deposition, a dielectric layer 113 may beconformally formed on the exposed surface of the floating gate 106.Specifically, the dielectric layer 113 is selectively formed mainly onthe exposed surface of the floating gate 106, with little or noformation of the dielectric layer 113 on the STI region 108 or any otherdielectric films under the identical plasma conditions (will bediscussed in detail below). With the dielectric layer 113 selectivelyformed mainly on floating gate 106, the reliability of the tunnel oxideand/or suppression of dopant diffusion out of the floating gate 106 areimproved while enabling scaling of the IPD film stack thickness.

The dielectric layer 113 may be a nitride layer such as silicon nitrideor silicon oxynitride. The nitride layer may be formed by exposing thefield surface 114 and sidewall 115 of the floating gate 106 to nitrogencontaining radicals. Nitrogen containing radicals, such as N, NH, NO,NH2, or NH3, may be created with the aid of some excitation, forinstance, a plasma excitation, a photo excitation, an electron-beamexcitation, or intense heat. Nitridation process may be performed bythermal means alone, by plasma means alone, or by a combination of thetwo. In one embodiment, the surfaces of the floating gate 106 areexposed to nitrogen containing radicals using a selective plasmanitridation process. The nitrogen containing radicals will reactpreferentially with the surface of the floating gate 106 (formed ofsilicon or polysilicon, for example) during the selective plasmanitridation process, rather than the surface of the STI region 108(formed of silicon oxide, for example) due to lower Si—Si bond-breakingenergies (222 kJ/mol) compared to Si—O bond-breaking energies (452kJ/mol). As radicals are not reactive enough to break Si—O bond, theselective plasma nitridation process forms nitrides of silicon fasterthan nitrides of silicon oxide, resulting in a significantly greaterconcentration of nitrogen-containing material, i.e., dielectric layer113 formed of, for example, Si—N bonds, at the field surface 114 andsidewall 115 of the floating gate 106 as opposed to STI region 108between the adjacent floating gates 106. Since the nitrogen-containingmaterial or dielectric layer 113 is not present in significant amountsat STI region 108, the undesired charge leakage path between neighboringfloating gate structures does not occur.

Radicals are preferred because ions have high chemical activity comparedto radicals and compared to the bond energies listed above (1stionization energy of N2=1402 kJ/mol; atomization energy of N2=473kJ/mol), so ions do not achieve the selectivity of radicals.Selectivity, defined as concentration of nitrogen in silicon divided byconcentration of nitrogen in oxide after a given deposition process, maybe between about 10:1 and about 100:1, such as between about 20:1 andabout 70:1, for example about 40:1. Greater exposure time may improvethe selectivity.

High radical density versus ion density may be achieved by a highpressure plasma process using, for example, a pressure between about 0.3Torr and 20 Torr, for example, about 5 Torr or above. The high pressureencourages ions to recombine with electrons quickly, leaving neutralradical species and inactive species. In some embodiments, a radical gasis formed. In some embodiments, remote plasma may be used to selectivelygenerate radical species by various methods. The remote plasmagenerator, for example a microwave, RF, or thermal chamber, may beconnected to a processing chamber through a delivery pipe. The deliverypipe, as will be described in more detail below with respect to FIGS. 3and 4, may be a relatively long pathway positioned at an angle relativeto the processing chamber to encourage recombination of ionic speciesalong the pathway before reaching the processing region. The radicalsflowing through the delivery pipe may flow into the chamber through ashowerhead or radical distributor, or through a portal entry in a sidewall of the chamber at a flow rate between about 1 slm and about 20 slm,such as between about 5 slm and about 20 slm, for example about 10 slm.Higher pressures and lower flows are believed to promote collisions.Nitrogen radicals may be formed in one embodiment by exposing a nitrogencontaining gas, such as nitrogen, ammonia, or a mixture thereof,optionally with a carrier gas such as helium, to microwave power betweenabout 1-3 kW at a pressure above about 5 Torr. The nitridation processmay be performed at a substrate temperature between about 300° C. andabout 1200° C., for example between about 800° C. and about 1000° C.,which may be increased as the nitridation proceeds to combat surfacesaturation. Heating may be performed using lamp heating, laser heating,use of a heated substrate support, or by plasma heating.

In certain embodiments, various ion filters, such as electrostaticfilters operated at a bias of, for example, about 200V (RF or DC), wireor mesh filters, or magnetic filters, any of which may have a dielectriccoating, may be used between the remote plasma source and the processingchamber. In other embodiments, residence time in the remote plasmagenerator may be modulated using gas flow of reactive species such asnitrogen containing species or gas flow of non-reactive species such asargon or helium. In some embodiments, radical half-life may be extendedby using an ion filter with low pressure plasma generation. Low pressureoperation may be facilitated by integrating a processing chamber with aremote plasma chamber without using an O-ring to seal the pathwaybetween the two chambers. Uniformity of radical flow into a processingchamber from remote plasma generation chamber may be improved using ashaped connector to provide intimate control of flow patterns.

The invention as described herein contemplates that substantially allions present in the plasma at the plasma generation (with the radicals)are eliminated prior to coming in contact with the surface of thefloating gate 106 (formed of silicon or polysilicon, for example) duringthe selective plasma nitridation process, rather than the surface of theSTI region 108 (formed of silicon oxide, for example). One waypositively charged ions are eliminated is by combining with electrons(also present in the plasma at the plasma generation) to return to anon-ionic or charge neutral state. A plasma may be substantially free ofthe majority of the ions by separating the plasma generation source fromthe substrate location, e.g., the reaction site, by a distance longerthan the lifetime of the ions at a given plasma discharge rate. In thismanner, the radicals survive the travel distance to the substrate, butions do not and instead lose their ionic character and become chargeneutral.

Exemplary Remote Plasma System

FIG. 2 illustrates an exemplary remote plasma system 200 may benefitfrom embodiments of the present invention. Particularly, the remoteplasma system 200 may be used to selectively form a nitride layer on asilicon or polysilicon surface of a semiconductor structure, such as aNAND flash memory device 100. The remote plasma system 200 may include arapid thermal processing (RTP) apparatus 201, such as Centura® RTPcommercially available from Applied Materials, Inc., located in SantaClara, Calif. Other types of thermal reactors may be substituted for theRTP apparatus such as, for example, RPN, RPO, Vantage RadiancePlus™ RTP,Vantage RadOX™ RTP, Radiance® RTP, or other similar chambers/reactorsavailable from Applied Materials Inc. of Santa Clara, Calif.

As can be seen in FIG. 2, coupled to the RTP apparatus 201 is a plasmaapplicator 280 used to remotely provide radicals of a plasma to the RTPapparatus 201. The RTP apparatus 201 generally includes a processingregion 213 enclosed by a side wall 214 and a bottom wall 215. The upperportion of side wall 214 may be sealed to a window assembly 217 by “0”rings. A radiant energy light pipe assembly 218 (enclosed by an upperside wall 224) is positioned over and coupled to window assembly 217.Light pipe assembly 218 may include a plurality of tungsten halogenlamps 219 each mounted into light pipes 221 and positioned to adequatelycover the entire surface area of wafer or substrate 101. Window assembly217 may include a plurality of short light pipes 241. A vacuum can beproduced in the plurality of light pipes 241 by pumping through a tube253 connected to one of the light pipes 241 which is in turn connectedto the rest of the pipes.

A wafer or substrate 101 containing the NAND flash memory device 100 issupported by a support ring 262 within a processing region 213. Supportring 262 is mounted on a rotatable cylinder 263. By rotating cylinder263, the support ring 262 and the wafer or substrate 101 are caused torotate during processing. Bottom wall 215 of RTP apparatus 201 may becoated or provided with a reflector 211 for reflecting energy onto thebackside of wafer or substrate 101. The RTP apparatus 201 may include aplurality of fiber optic probes 271 positioned through the bottom wall215 of RTP apparatus 201 to detect the temperature of the wafer orsubstrate.

The plasma applicator 280 generally includes a body 282 surrounding atube 284 where a plasma of ions, radicals, and electrons is generated.The tube 284 may be made of quartz or sapphire. The tube 284 preferablydoes not form any electrical bias that might attract charged particles,e.g., ions. A gas inlet 286 is disposed at one end of the body 282 andopposes to a gas outlet 288 that is located at the other end of the body282. The gas outlet 288 is in fluid communication with the RTP apparatus201 through a delivery pipe 290 such that radicals of the plasmagenerated within the tube 284 are supplied to the processing region 213of the RTP apparatus 201. The gas outlet 288 may have a diameter largerthan gas inlet 286 to allow the excited radicals to be efficientlydischarged at desired flow rate and to minimize the contact between theradicals and the tube 284. If desired, a separate orifice may beinserted into tube 284 at the gas outlet 288 to reduce the tube's innerdiameter. The diameter of the gas outlet 288 (or orifice, if used) canbe selected to optimize the pressure differential between the processingregion 213 and the plasma applicator 280 for nitridation efficiency.

A gas source 292 of nitrogen-containing gas, including, but not limitedto, N₂ gas, may couple to a gas inlet 286 via a first input of athree-way valve 294 and a valve 297 used to control the flow rate of gasreleased from the gas source 292. A second input of the three-way valve299 may be coupled to another process gas source 298 including, but notlimited to, oxygen-containing gas, silicon-containing gas, or inner gas.A flow controller 296 is connected to the three-way valve 294 to switchthe valve between its different positions, depending upon which processis to be carried out. The flow controller 296 also functions in asimilar fashion to control the three-way valve 294 and the valve 317 toprovide an appropriate process gas flow from gas source 298 to theprocess chamber.

The plasma applicator 280 may be coupled to an energy source (not shown)to provide an excitation energy, such as an energy having a microwavefrequency, to the plasma applicator 280 to excite the process gastraveling from the gas source 292 into a plasma. In the case wherenitrogen-containing gas, for example, N₂, is used, the microwaveexcitation in plasma applicator 280 produces N* radicals, positivelycharged ions such as N⁺ and N₂ ⁺, and electrons in the tube 284. Bylocating the plasma applicator 280 remotely from the processing region213 of RTP apparatus 201, a plasma source can be selectively generatedto limit the composition of the plasma exposed to substrate 101 topredominantly radicals. It has been observed that ions collisions can befurther promoted by using an improved delivery pipe 290 such that all orthe majority of ions generated by the excitation of the process gas toform a plasma outlive their ionic lifetime and become charge neutralbefore reaching the processing region 213. In other words, thecomposition of the plasma that is supplied to the inlet port 275 of theRTP apparatus 201 is predominantly radicals.

FIG. 3 illustrates a schematic and fragmentary cross-sectional side viewof an exemplary delivery pipe 300 that may be used in place of thedelivery pipe 290 of FIG. 2 according to one embodiment of the presentinvention. For the purpose of simplicity and clarity of illustration,elements in the drawings have not been drawn to scale. The delivery pipe300 generally includes a mounting sleeve 302 and an inlet member 304connecting to the mounting sleeve 302. The mounting sleeve 302 and theinlet member 304 each include a hollow cylindrical body defining alongitudinally extending space, for example, sleeve passageway 306 andinlet passageway 308. The profile of the passageway 306, 308 may be anyshape such as circular, oval, square, rectangular, or irregular. One endof the mounting sleeve 302 may be bolted to the gas outlet 288 of thebody 282 of the plasma applicator 280 (partially shown) so that thesleeve passageway 306 in the mounting sleeve 302 is aligned with andcoupled to the tube 284 at the gas outlet 288. Another end of themounting sleeve 302 is connected to the inlet member 304 so that theinlet passageway 308 in the inlet member 304 is substantially alignedwith the sleeve passageway 306 in the mounting sleeve 302. In certainexamples, the diameter of the mounting sleeve 302 may be graduallyreduced along the longitudinal axis of the mounting sleeve 302 to matchthe diameter of the inlet member 304. The mounting sleeve 302 and theinlet member 304 may be made of a material that does not causerecombination of the N* radicals. For example, the mounting sleeve 302and the inlet member 304 may be made of silicon, silicon nitride, boronnitride, carbon nitride, sapphire or alumina (Al₂O₃). While the deliverypipe 300 is shown and described as two separate components (i.e., themounting sleeve 302 and the inlet member 304) being connected to oneanother, the invention contemplates a delivery pipe formed from asingle-piece integrated body with a passageway connecting to the inletport 275 of the RTP apparatus 201.

As can be better seen in FIG. 4, which illustrates a schematic andfragmentary top view of the delivery pipe 300 and the RTP apparatus 201,the inlet member 304 may be configured as an adapter which is coupled tothe inlet port 275 in the side wall 214 of the RTP apparatus 201. Itshould be noted that some elements in FIG. 4 have been omitted and notdrawn to scale for the purpose of simplicity and clarity ofillustration. The inlet member 304 may include a flange 310 extendingwholly around the outer surface of the inlet member 304. A portion ofthe inlet member 304 may be extended into the side wall 214 such that anoutermost face 312 of the flange 310 is bolted to the interior surface214 b of the side wall 214. Alternatively, the outermost face 312 of theflange 310 may be bolted to the exterior surface 214a of the side wall214 and configured in a way that the inlet passageway 308 is coupled tothe inlet port 275. In either case, the delivery pipe 300 is coupled tothe inlet port 275 in such a way that a longitudinal axis “A” of theinlet passageway 308 in the inlet member 304 intersect at an angle θwith respect to a longitudinal axis “B” of the inlet port 275. Theflange 310 may extend in a direction at a desired angle “α” relative tothe longitudinal axis “A” of the inlet passageway 308 as long as thatthe outermost face 312 of the flange 310 is substantially flush withinterior surface 214 b of the side wall 214.

In one embodiment, the angle “α” may range from about 20 degrees toabout 80 degrees, such as about 45 degrees to about 70 degrees. Theangle θ between the longitudinal axis “A” of the inlet passageway 308and the longitudinal axis “B” of the inlet port 275 may range betweenabout 10 degrees and about 70 degrees, such as about 20 degrees andabout 45 degrees. In one example, the angle α is about 45 degrees orabove, for example about 60 degrees. The angle α or θ should not belimited as defined herein and may vary as necessary. Having the deliverypipe 300 positioned at an angle relative to the inlet port 275 promotescollision of ions or reaction of ions with electrons or other chargedparticles since the ions lose their momentum through collisions whenhitting the interior surface of the inlet port 275. Therefore,substantially all ions created by the excitation by the energy sourceare eliminated prior to entering the processing region 213. While thedelivery pipe 300 is shown and described to include the flange 310, theflange 310 may be omitted as long as the delivery pipe 300 is coupled tothe RTP apparatus 201 at an angle that would promote collision of ionsor reaction of ions with electrons or other charged particles.

In addition to the bent pipe structure as described herein, the deliverypipe 300 may be constructed of a length such that, for a given flow rateof a process gas (e.g., a given plasma generation rate), substantiallyall ions are extinguished or reacted with electrons or other chargedparticles to lose their excited state prior to existing the deliverypipe 300. The length of tube 284 and delivery pipe 300 necessary toextinguish substantially all the ions of a plasma at a given source gasflow rate may be determined experimentally or by lifetime calculations.In one embodiment, the tube 284 may have a length of about 5 inches toabout 12 inches with an inside diameter of about 0.5 inches to about 2inches. The length of the delivery pipe 300 (including passageways 306,308) may vary from about 5 inches to about 25 inches, for example about16 inches or above. The diameter of the passageway 306, 308 may beadjusted to optimize the pressure differential between the plasmaapplicator 280 and the processing region 213. In one embodiment, thediameter of the passageway 306, 308 is in a range between about 0.5inches and about 2 inches, for example about 0.65 inches and about 1.5inches in diameter. If desired, either one or both of the passageways306, 308 may have a diameter gradually decreasing or increasing in thedirection of flow to promote ion loss. In various embodiments, the totallength of the tube 284 and the delivery pipe 300 may be between about 8inches to about 35 inches, for example about 20 inches to about 35inches. It is believed that a converging flow of plasma will promoteions collisions. The compression ratio, defined as cross sectional areaof plasma generation area, (e.g., the tube 284) to cross sectional areaof smallest diameter before the inlet port 275 (e.g., the inletpassageway 308) may be about 2 or above, for example between about 5 andabout 10.

By separating the plasma generation area (i.e., plasma applicator 280)and the processing region 213 physically with an improved delivery pipe300 being positioned at an angle relative to an inlet port 275 of theRTP apparatus that promotes recombination of ionic species, greaterselectivity of nitridation of silicon or polysilicon floating gate 106is obtained. In an embodiment where a NAND flash memory device having afloating gate 106 with silicon or polysilicon surface is treated with aselective nitridation process performed by the apparatus describedherein, selectivity of nitridation of silicon or polysilicon floatinggate 106 to STI region 108 may be increased to up to about 100:1 with anitrogen dose of about 5×1015 atoms/cm2 to about 15×1015 atoms/cm2, suchas about 20×1015 atoms/cm2 or up, for example about 25×10¹⁵ atoms/cm²,in the surface of silicon or polysilicon floating gate 106.

Exemplary Remote Plasma Radical Treatment of Gate Oxides

As discussed above, the manufacturers of NAND Flash memories need alower thermal budget solution to incorporate nitrogen at the interfacebetween the floating gate and the tunnel oxide. It has been observed bythe inventors that the thermal budget for the nitrogen incorporation inthe surface of the floating gate can be lowered by using radicalactivation of species. FIG. 5 depicts a method 500 of fabricating a NANDflash memory device according to one embodiment of the presentinvention. The method 500 is illustratively described with reference toFIGS. 6A-6C, which depicts stages of fabrication of a NAND flash memorydevice 600 in accordance with the embodiments of the method 500. Themethod 500 includes a radical nitridation process to incorporatenitrogen into exposed surfaces of the tunnel oxide followed by afloating gate formation process.

The method 500 generally begins at 502 by introducingnitrogen-containing gas into a remote plasma applicator which is drivenwith, for example, microwave, RF, or thermal energy. In one embodiment,the nitrogen-containing gas is introduced into the plasma applicator 280as depicted in FIG. 2. The remote plasma generator may be connected to aprocessing chamber, for example, a rapid thermal processing (RTP)apparatus 201 as depicted in FIG. 2, through a delivery pipe. Thedelivery pipe may be positioned at an angle relative to an inlet port ofthe RTP apparatus, as discussed above with respect to FIGS. 3 and 4, soas to promote recombination of ionic species. The nitrogen-containinggas may be provided from a gas source, for example, the gas source 292depicted in FIG. 2. In various embodiments, the nitrogen-containing gasmay include, but is not limited to, nitrogen (N₂), nitric oxide (NO),nitrous oxide (N₂O), nitrogen dioxide (NO₂), ammonia (NH₃), hydrazine(N₂H₄), and mixtures thereof. In certain embodiments, thenitrogen-containing gas may include a gas mixture comprising NH₃ and N₂,a gas mixture comprising NH₃ and H₂, a gas mixture comprising NH₃, N₂,and H₂, or a gas mixture comprising N₂ and H₂. In certain embodiments,hydrazine (N₂H₄) may be used in place of or in combination with NH₃ inthe gas mixture with N₂ and H₂. Alternatively, the nitrogen-containinggas may include lower substituted hydrazines (N₂R₂, wherein each R isindependently hydrogen, a methyl, ethyl, propyl, vinyl, or propenylgroup), and lower amines (NR_(a)H_(b), wherein a and b are each integersfrom 0 to 3 and a+b=3, and each R is independently hydrogen, a methyl,ethyl, propyl, vinyl, or propenyl group), amides (RCONR′R″, wherein R,R′, and R″ are each independently hydrogen, a methyl, ethyl, propyl,vinyl, or propenyl group), imines (RR′C═NR″, wherein R, R′, and R″ areeach independently hydrogen, a methyl, ethyl, propyl, vinyl, or propenylgroup), or imides (RCONR′COR″, wherein R, R′, and R″ are eachindependently hydrogen, a methyl, ethyl, propyl, vinyl, or propenylgroup). The nitrogen-containing gas may be optionally mixed withnon-reactive gases, such as one or more of nitrogen gas (N₂), helium(He), argon (Ar), neon (Ne), xenon (Xe), or the like.

At box 504, the nitrogen-containing gas in the plasma applicator 280 isexcited to produce nitrogen-containing radicals such as N, NO, NH, orNH₂. The nitrogen-containing gas may be exposed to a plasma in order toenhance the radical generation. The nitrogen-containing gas may beactivated by exposure to an excitation energy such as microwave, UV, RF,intense heat, or electron synchrotron radiation. In one embodiment, theplasma applicator 280 is coupled to a microwave source having amicrowave frequency to excite and dissociate the nitrogen-containing gastraveling from the gas source 292 into a plasma containingnitrogen-containing radicals. In one embodiment, the microwave source isa 2.45 GHz microwave source. The microwave source may be operated at apower level between about 1,000 W and 5,000 Watts, for example, 3,000Watts.

High radical density versus ion density may be achieved by a highpressure plasma process using, for example, pressure between about 1Torr and about 10 Torr. The high pressure is believed to encourage ionsto recombine with electrons quickly, leaving neutral radical species andinactive species. In the case where ammonia gas (NH₃) is used to producenitrogen-containing radicals, the ammonia gas may be excited anddissociated in plasma applicator 280 to yield a plasma containing N*radicals, H* radicals, and/or NH* radicals. The excitation of ammoniagas may be performed at low microwave power between about 1 kW to about3 kW. At low power, less dissociation of ammonia produces NHx* radicalswithout substantially dissociate the ammonia molecule. Therefore, moreNHx* radicals can be delivered to the rapid thermal processing (RTP)apparatus 201, thereby limiting the composition of the plasma exposed tothe device 100 to predominantly NHx* radicals.

At box 506, the plasma comprising substantially of nitrogen-containingradicals is flowed into the processing region 213 of the RTP apparatus201 where semiconductor device is disposed. In one embodiment, thesemiconductor device is a partially fabricated NAND flash memory devicehaving a tunnel oxide. The plasma is substantially free of the majorityof the ions by separating the plasma generation area (i.e., plasmaapplicator 280) from the processing region 213 by a distance longer thanthe lifetime of the ions at a given plasma discharge rate, and by usingan improved delivery pipe 300 positioned at an angle relative to aninlet port 275 of the RTP apparatus that promotes recombination of ionicspecies, as discussed above with respect to FIGS. 2-4. The partiallyfabricated NAND flash memory device 600 is generally illustrated in FIG.6A, which include a substrate 602 (similar to the substrate 102 depictedin FIG. 1) having a tunnel oxide layer 604 (similar to the tunnel oxidelayer 104 depicted in FIG. 1) disposed thereon. A shallow trenchisolation region 608 (similar to the STI region 108 depicted in FIG. 1)may be disposed adjacent to the tunnel oxide layer. The tunnel oxidelayer 604 may include silicon and oxygen, such as silicon oxide (SIO₂),silicon oxynitride (SiON), or high-k dielectric materials, as discussedabove with respect to FIG. 1. The exposure of the surface 605 of thetunnel oxide layer 604 to nitrogen-containing radicals results in a highnitrogen incorporation in the exposed surface 605 of the tunnel oxidelayer 604, forming a nitrogen region 603 as shown in FIG. 6B. In oneembodiment, the nitrogen region 603 may have a thickness between about0.1 nm and about 5 nm. The nitrogen region 603 may have a nitrogenconcentration of about 4%, for example, about 8% or above. The nitrogenregion 603 may act as a barrier layer and prevent dopant in thesubsequently formed floating gate 606 from diffusing through the tunneloxide layer 604.

The nitrogen-containing radicals may flow into the processing region 213at a flow rate between about 1 slm and about 20 slm, such as betweenabout 5 slm and about 20 slm, for example about 10 slm. During theprocess of nitrogen incorporation, the partially fabricated NAND flashmemory device 600 may be positioned in a processing region of a processchamber, for example, the rapid thermal processing (RTP) apparatus 201,under a non-reactive atmosphere and subjected to a temperature betweenabout 300° C. to about 1050° C. In cases where activated NH* radicalsare delivered into the RTP apparatus 201, the temperature of thesubstrate 602 may be maintained between about 400° C. to about 1000° C.In cases where activated NO* radicals are delivered into the RTPapparatus 201, the temperature of the substrate 602 may be maintainedbetween about 800° C. to about 1000° C. Gases which are considerednon-reactive include, but are not limited to, nitrogen gas (N₂), helium(He), argon (Ar), neon (Ne), and xenon (Xe). Pressure in the processingregion of the RTP apparatus 201 may be controlled between about 0.1 Torrand 50 Torr, for example between about 2 Torr to about 20 Torr, such asbetween about 5 Torr to 10 Torr.

At box 508, a conductive material, such as silicon, polysilicon, metals,or the like, is deposited atop the tunnel oxide layer to form a floatinggate 606 (similar to the floating gate 106 depicted in FIG. 1), as shownin FIG. 6C. While not discussed here, other fabrication steps used tocomplete the NAND flash memory device are contemplated. An exemplaryNAND flash memory device is generally depicted in FIG. 1. The processdescribed herein enables incorporation of nitrogen at the interfacebetween the floating gate 606 and the tunnel oxide 604 by reactingactivated nitrogen-containing radicals at exposed surface 605 of thetunnel oxide layer 604, thus improving the film electrical properties atlower thermal budgets less than 1000° C.

FIG. 7 depicts a method 700 of fabricating a NAND flash memory deviceaccording to another embodiment of the present invention. The method 700is illustratively described with reference to FIGS. 6A-6D, which depictsstages of fabrication of a NAND flash memory device 600 in accordancewith the embodiments of the method 700. The method 700 includes aradical nitridation process to incorporate nitrogen into exposedsurfaces of the tunnel oxide followed by a floating gate formationprocess.

The method 700 generally begins at 702, where a partially fabricatedNAND flash memory device having a tunnel oxide layer may be provided toa processing region of a processing chamber, for example, the rapidthermal processing (RTP) apparatus 201 as depicted in FIG. 2. Thepartially fabricated NAND flash memory device is illustrated in FIG. 6Aas discussed above.

At box 704, a nitrogen-containing gas is flowed into the processingregion 213 of the RTP apparatus 201 where the partially fabricated NANDflash memory device 600 is disposed. The partially fabricated NAND flashmemory device 600 having the tunnel oxide layer 604 is exposed to thenitrogen-containing gas. The nitrogen-containing gas may be similar tothe nitrogen-containing gas as discussed above in box 502. In oneembodiment, the nitrogen-containing gas includes ammonia (NH₃). Inanother embodiment, the nitrogen-containing gas includes nitric oxide(NO). The RTP apparatus 201 may be operated at a pressure between about1 Torr and about 5 Torr.

At box 706, a gas mixture containing a nitrogen-containing gas is flowedinto a remote plasma applicator, for example, the plasma applicator 280as depicted in FIG. 2. The remote plasma generator may be connected tothe RTP apparatus 201 through a delivery pipe to promote recombinationof ionic species before entering the processing region, as discussedabove with respect to FIGS. 3 and 4. In various embodiments, thenitrogen-containing gas may include, but is not limited to, nitrogen(N₂), nitric oxide (NO), nitrous oxide (N₂O), nitrogen dioxide (NO₂),ammonia (NH₃), hydrazine (N₂H₄), and mixtures thereof. Alternatively,the gas mixture may include non-reactive gases such as helium (He),argon (Ar), neon (Ne), xenon (Xe), or the like. In certain embodiments,the gas mixture may include both the nitrogen-containing gas andnon-reactive gases.

At box 708, the gas mixture in the plasma applicator 280 is excited toproduce nitrogen-containing radicals such as N, NO, NH, or NH₂ and/orradicals from non-reactive gases such as He* or Ar* etc. The dissociatedgas mixture may contain free radicals such as N* radicals, N₂* radicals,Ar*, He* radicals, ions, atoms, and molecules thereof, and electrons,depending upon the gas mixture chosen. The gas mixture may be activatedby exposure to an excitation energy such as microwave, UV, RF, intenseheat, or electron synchrotron radiation. In one embodiment, the gasmixture is exposed to a 2.45 GHz microwave source operating at a powerlevel between about 1,000 W and 5,000 Watts, for example, about 3,000Watts, at a pressure about 1 Torr and about 10 Torr.

At box 710, the plasma comprising substantially of nitrogen-containingradicals and/or radicals from non-reactive gases is flowed into theprocessing region 213 of the RTP apparatus 201 where the partiallyfabricated NAND flash memory device 600 having the tunnel oxide 604 isdisposed in the presence of the nitrogen-containing gas. The plasmacomprising substantially of nitrogen-containing radicals and/or radicalsfrom non-reactive gases may flow into the processing region at a flowrate between about 1 slm and about 20 slm, such as between about 5 slmand about 20 slm, for example about 10 slm. During the process ofnitrogen incorporation, the partially fabricated NAND flash memorydevice 600 may be positioned in the processing region under anon-reactive atmosphere. Gases which are considered non-reactiveinclude, but are not limited to, nitrogen gas (N₂), helium (He), argon(Ar), neon (Ne), and xenon (Xe). Pressure in the processing region ofthe RTP apparatus 201 may be controlled between about 0.1 Torr and 50Torr, for example between about 2 Torr to about 20 Torr, such as betweenabout 5 Torr to 10 Torr.

The plasma containing substantially of N* radicals, N2* radicals, Ar*radicals, or He* radicals (may vary depending upon the gas mixturechosen) may react with the NH₃ gas or NO gas that is previously filledwithin the processing region 213 through an alternate gas inject (notshown in FIG. 4) to produce N* radicals, H* radicals, NO radicals,and/or NH* radicals. In cases where the RTP apparatus 201 is previouslyfilled with NO gas, the temperature of the substrate 602 may bemaintained between about 800° C. to about 1000° C. during thenitridation process. In cases where the RTP apparatus 201 is previouslyfilled with NH₃ gas, the temperature of the substrate 602 may bemaintained between about 400° C. to about 1000° C. during thenitridation process. The excitation of NH₃ gas may be performed at lowmicrowave power between about 1 kW to about 3 kW without substantiallydissociate the ammonia molecule. Therefore, the partially fabricatedNAND flash memory device 600 is exposed predominantly to NHx* radicals.

The exposure of the surface 605 of the tunnel oxide layer 604 to thesenitrogen-containing radicals results in a high nitrogen incorporation inthe exposed surface 605 of the tunnel oxide layer 604, forming anitrogen region 603 as shown in FIG. 6B. In one embodiment, the nitrogenregion 603 may have a thickness between about 0.1 nm and about 5 nm. Thenitrogen region 603 may have a nitrogen concentration of about 4%, forexample, about 8% or above. The nitrogen region 603 may act as a barrierlayer and prevent dopant in the subsequently formed floating gate 606from diffusing through the tunnel oxide layer 604.

In an alternative embodiment shown in FIG. 6D, prior to the depositionof the tunnel oxide layer 604, a surface 607 of the substrate 602 may beexposed to plasma activated species generated from a nitrogen-containinggas such as NO or N₂O to incorporate nitrogen (denoted as 610) in theexposed surface 607. With the subsequent nitridation process asdescribed with respect to FIGS. 5 and 7, the interface between thesubstrate 602 and the tunnel oxide layer 604 and the interface betweenthe tunnel oxide layer 604 and the subsequently formed floating gate 606may both provide a nitrogen region 603, 610 to further improve the NANDflash program window.

At box 712, a conductive material, such as silicon, polysilicon, metals,or the like, is deposited atop the tunnel oxide layer to form a floatinggate 606 (similar to the floating gate 106 depicted in FIG. 1), as shownin FIG. 6C. While not discussed here, other fabrication steps used tocomplete the NAND flash memory device are contemplated. An exemplaryNAND flash memory device is generally depicted in FIG. 1. The processdescribed herein enables incorporation of nitrogen at the interfacebetween the floating gate 606 and the tunnel oxide 604 by reactingactivated nitrogen-containing radicals at exposed surface 605 of thetunnel oxide layer 604, thus improving the film electrical properties atlower thermal budgets less than 1000° C.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A method for processing a semiconductordevice in a processing chamber, comprising: generating a plasmacomprising nitrogen-containing radicals in a remote plasma applicator;flowing the plasma comprising nitrogen-containing radicals into aprocessing region of the processing chamber where the semiconductordevice is disposed, wherein the semiconductor device comprises asubstrate having an oxide layer formed thereon, comprising: flowing theplasma comprising nitrogen-containing radicals from the remote plasmaapplicator into a delivery member having a longitudinal passageway; andflowing the plasma comprising nitrogen-containing radicals from thepassageway to an inlet port formed in a sidewall of the processingchamber, wherein the delivery member is configured such that alongitudinal axis of the passageway intersects at an angle of about 20degrees to about 80 degrees with respect to a longitudinal axis of theinlet port such that the plasma is flowed at an angle into the inletport to promote collision of ions or reaction of ions with electrons orcharged particles in the plasma to substantially eliminate ions from theplasma before entering the processing region of the processing chamber;exposing an exposed surface of the oxide layer to thenitrogen-containing radicals; and incorporating nitrogen in the exposedsurface of the oxide layer of the substrate.
 2. The method of claim 1,wherein the passageway has a length between about 5 inches and about 25inches.
 3. A method for processing a semiconductor device in aprocessing chamber, comprising: exposing the semiconductor device to anitrogen-containing gas, wherein the semiconductor device has asubstrate comprising a oxide layer formed thereon; flowing a gas mixturecomprising nitrogen-containing gas and/or a non-reactive gas into aremote plasma applicator; exciting the gas mixture to produce a plasmacomprising nitrogen-containing radicals and/or radicals from thenon-reactive gas; flowing the plasma comprising nitrogen-containingradicals and/or radicals into the processing region of the processingchamber where the semiconductor device is disposed in the presence ofthe nitrogen-containing gas to activate the nitrogen-containing gas,comprising: flowing the plasma comprising nitrogen-containing radicalsand/or radicals from the non-reactive gas from the remote plasmaapplicator into a delivery member having a longitudinal passageway; andflowing the plasma comprising nitrogen-containing radicals and/orradicals from the non-reactive gas from the passageway to an inlet portformed in a sidewall of the processing chamber, wherein the deliverymember is configured such that a longitudinal axis of the passagewayintersects at an angle of about 20 degrees to about 80 degrees withrespect to a longitudinal axis of the inlet port such that the plasma isflowed at an angle into the inlet port to promote collision of ions orreaction of ions with electrons or charged particles in the plasma tosubstantially eliminate ions from the plasma before entering theprocessing region of the processing chamber; exposing an exposed surfaceof the oxide layer to the nitrogen-containing radicals generated fromthe activated nitrogen-containing gas; and incorporating nitrogen in theexposed surface of the oxide layer of the substrate.
 4. The method ofclaim 3, wherein the delivery member is disposed between the remoteplasma applicator and the processing chamber.
 5. The method of claim 3,wherein the passageway has a length between about 5 inches and about 25inches.